Circuit breaking device for very high temperature

ABSTRACT

A snap action, non-resettable circuit breaking device accurately operable at very high temperatures. Its structure is comprised of two strips secured to a support and extending therefrom. The free ends of each strip engage one another. A set of contacts is so connected to the strips that the contacts are closed to complete a circuit only when the ends are engaged. One strip is a spring and the other strip is a temperature sensitive device, such as a bimetal. The contacting ends are movable in intersecting arcs and the spring is maintained in a biased state by the bimetal when the two are in contact. As the bimetal deflects in response to heat it bends the spring further away from its unbiased position. At the point where the intersecting arcs coincide the spring will snap away from the bimetal thus opening the contacts and breaking the circuit.

United States Patent [191 Hickling CIRCUIT BREAKING DEVICE FOR VERY HIGH TEMPERATURE Colin D. Hickling, Woodstock, NY.

[73] Assignee: American Thermostat Corporation, South Cairo, NY.

22 Filed: Oct. 7, 1974 21 Appl. No.: 512,497

[ 75] Inventor:

Primary ExaminerL. T. Hix Assistant ExaminerFred E. Bell [57] ABSTRACT A snap action, non-resettable circuit breaking device accurately operable at very high temperatures. Its structure is comprised of two strips secured to a support and extending therefrom. The free ends of each strip engage one another, A set of contacts is so connected to the strips that the contacts are closed to complete a circuit only when the ends are engaged. One strip is a spring and the other strip is a temperature sensitive device, such as a bimetal. The contacting ends are movable in intersecting arcs and the spring is maintained in a biased state by the bimetal when the two are in contact. As the bimetal deflects in response to heat it bends the spring further away from its unbiased position. At the point where the intersecting arcs coincide the spring will snap away from the bimetal thus opening the contacts and breaking the circuit.

15 Claims, 4 Drawing Figures Sheet 1 of 2 3,913,052

US. Patent Oct. 14, 1975 FIG! FIG. 2

US. Patent 'Oct.14,1975 Sheet20f2 3,913,052

CIRCUIT BREAKING DEVICE FOR VERY HIGH TEMPERATURE The present invention relates to a novel temperature responsive circuit breaking device accurately operable at very high temperatures.

Many requirements exist for a circuit breaking device that can be set to operate at temperatures up to 900 F and having such other desirable characteristics as non-resettability, accuracy, insignificant drift of the cut-out temperature with age, compactness, simplicity and low cost. A self-cleaning oven, for example, is one possible application. Similar applications would normally involve equipment regulated at very high operating temperatures. Should the equipment malfunction and the temperature exceed the operating temperature, however, the added heat might damage the equipment, its surroundings or its operating personnel; To prevent such damage yet permit high operating temperatures is one task of the invention.

The commonly used temperature responsive circuit breaking device is a fuse containing an element which melts and thereby interrupts the circuit at a certain temperature. However, the temperature responsive material in these fuses melts at relatively low temperatures and is not practically usable at very high temperatures. To meet high operating temperature requirements, the prior art solutions dealt with development of various types of the melting material in fuses. The material with the highest temperature setting to my knowledge is eutectic solder but it has a practically usable temperature setting of only 400 F. If this eutectic solder is made so that it can be set to operate above 400 F its characteristics are subject to change with age and thus the cut-out temperature cannot be reliably set. Furthermore, all fuses have the additional disadvantage, in ambient temperature sensing devices, of electric current passing through the temperature responsive element. Since this current causes heat in addition to the ambient condition due to the presence of resistance in the element, the maximum settable ambient temperature for the circuit breaker is commensurately reduced.

To eliminate these disadvantages of the standard fuse the present invention involves a mechanical separation of two contacts. No melting is involved and power need not be carried by the temperature sensitive element. Furthermore, the mechanical separation allows operation at much higher temperatures than possible with the melting materials. However, a problem common to many mechanical contact breaking devices is sticking of the contacts due to welding. This problem is further aggravated by the high temperatures contemplated for the invention. Contact sticking must be successfully dealt with since otherwise the circuit will either fail to be interrupted or interruption will be delayed with possible serious damage to equipment and personnel.

It is a general object of the invention to provide an improved temperature responsive circuit breaking device.

It is a more specific object ofthe invention to provide a circuit breaking device with a cut-out point accurately settable at very high temperatures.

It is another object of the invention to provide a circuit breaking device which combines an accurate high temperature cut-out with such other desirable features as insignificant drift of the cut-out temperature with age, accuracy, compactness, simplicity and low cost.

It is a further object of the present invention to provide a temperature responsive circuit breaking device which cannot be reset except by gross mechanical distortion.

It is a still further object of the invention to devise a reliable temperature responsive circuit breaking device to insure interruption of the circuit at the cut-out temperature.

In accordance with these objects a circuit breaking device is provided having two solid strips connected to a set of contacts. One end of each strip is fastened to a support and the other ends extend away from the support and the engaged ends keep a set of contacts closed to complete a circuit. One strip is a spring made of a material which maintains its characteristics at very high temperatures while the other is a temperature sensitive device such as a bimetal. When the strip ends are engaged the bimetal maintains the spring biased away from its free rest position. As the bimetal deflects due to heat, it biases the spring further away from its free rest position. The two strips are so positioned that this deflection also causes the engaged ends to slide against each other. This sliding motion is the result, then, of two opposing forces and sticking is much less likely. Separation of the engaged ends and consequent opening of the set of contacts is attained by providing for the movement of the ends in intersecting arcs. At the point of intersection the strips have moved until only their very tips are touching. A slight further deflection of the bimetal allows the spring to snap away to its free rest position. In this position it is completely detached from the bimetal. Contact cannot be re-established except by gross mechanical distortion. The sliding and snap actions are facilitated by appropriately shaping the spring and by the manner in which the ends of the bimetal and spring are engaged.

The circuit breaking device is adaptable for use for current sensing and/or temperature sensing. The latter usage involves use of the bimetal to detect only ambient temperatures. It does not conduct current. Current is carried by the spring and a conductor in contact with the spring. As the spring snaps away from the bimetal, as discussed above, it also breaks contact with the conductor to interrupt the circuit.

To the accomplishments of the above, and to such other objects as mayhereinafter appear, the present invention relates to a circuit breaking device operable at high temperatures and having an element which responds to heat by bending a spring away from its free rest position to enable a strong sliding and consequent snap action separation of the spring from the element at a predetermined temperature, all as defined in the appended claims and as described in this specification taken together with the accompanying drawings, in which:

FIG. 1 shows an embodiment of the invention wherein the temperature sensitive element conducts current;

FIG. 2 is a view of the embodiment of FIG. 1 showing the spring and bimetal after the snap action has occurred;

FIG. 3 is another embodiment of the present invention wherein the temperature sensitive element does not conduct current; and

FIG. 4 is still another embodiment of the present invention wherein the temperature sensitive element does not conduct current.

DETAILED DESCRIPTION OF THE DRAWINGS The circuit breaker arrangement of FIG. 1 comprises two strips 2 and 3 secured at one end to a support, 1, (shown in cross-section) made of non-conductive material. Strip 2 has its free end, shown generally by 14, bent in a partial circle and is made of a resilient material so that it acts like a spring in tending to return toward its position in FIG. 1 when bent upward. If strip 2 is bent, its tip P1 follows arc C1. The effective center of this arc is at point P4 and its location depends on such factors as stiffness of the spring, the biasing point (place where it is bent) and the spot where it is secured to the support 1. Strip 2 is a temperature responsive element, such as a bimetal, and is relatively straight at room temperature. When heat is applied it deflects upward and its tip follows are C2. The point P3 is the effective center for are 02 and its location is dependent on such factors as the metal characteristics of the bimetal and the point where it is secured to the support 1. The strips 2 and 3 are so assembled on the support as to have their free ends touching and slightly overlapping at C. The amount of overlap is the distance between PI and P2. Leads and 16 are connected to strips 2 and 3, respectively, and carry current to the load (not shown).

In operation, current is supplied to the load by way of lead 15, spring 2 electrically connected to lead 15, bimetal 3 and lead 16 electrically connected to bimetal 3. The bimetal 3 responds to either current or ambient temperature or both by deflecting upward. As it does so it also forces the spring 2 upward. As each strip bends, the tips P1 and P2 follow intersecting arcs C1 and C2, respectively. Since these tips follow intersecting arcs, a sliding action results between the strips at the contacting ends. This sliding movement is facilitated by the geometric configuration at the point of contact C to diminish the frictional forces. The slight bend of P1 away from strip 3 provides a smaller friction surface and a smooth path for P2 to travel. The tip P2 will slide progressively closer to P1 as the bimetal deflects upward while P1 will slide closer to P2 due to the propensity of the spring to return to its original position in FIG. 1. The sliding action is the result, then, of two opposing forces and sticking of the contacting ends due to welding or frictional force is accordingly less likely. As the point of intersection of the arcs, P5, is reached, the points P1 and P2 will be barely touching. A slight further deflection of the bimetal will enable spring 2 to snap back toward its original position. Contact between the two strips will thereby be broken and the circuit will be interrupted.

To prevent possible circuit reset when the bimetal cools and to provide a stronger slide and snap action, the strip 2 is bent at A as shown in FIG. 2. Additional force is now provided by the spring because this force is directly proportional to the distance of the spring from its free rest position. The bend at A increases this distance when the two strips are assembled as shown in FIG. 1 with spring 2 being biased well away from the free rest position. As heat is applied to bimetal 3 the strip ends follow the arcs shown in FIG. 1 until they snap apart when the bimetal is in the position of 3 corresponding to its tip being at P5 in FIG. 1. Due to the additional bias on strip 2 more force is now available to prevent sticking at the point of contact as the strips slide over each other. The free rest position of strip 2 is such that no flexing of the bimetal 3, shown in its room temperature position by 3, under foreseen conditions, and only gross mechanical distortion, will bring the two strips in contact and reset the circuit even after the bimetal 3 has cooled and returned to its original straight position. More reliability both as to the sticking problem and circuit reset is thus economically afforded by this embodiment with no increase in complexity or the number of parts.

The previous embodiment involves the flow of current through the bimetal. If the application requires the sensing of ambient temperatures, however, such curent conduction by the bimetal is disadvantageous, as discussed above with respect to fuses. Heat inherently results from such current flow thereby limiting the settable range of the circuit breaker to the maximum operable temperature of the device minus the heat generated by current through the bimetal. In high power applications, especially, such self generated heat by the bimetal due to current is considerable. The elimination of this heat source is, therefore, an important advantage of any circuit breaker used in applications requiring very high ambient operating temperatures of up to 900 F.

FIG. 3 shows a circuit breaker designed to provide a maximum ambient temperature range. No current is carried by the bimetal 3. Instead a conductive strip 4 is provided with a lead 11. Spring 2 has a bent portion at B which comes in contact with the strip 4. Lead 12 is connected to strip 2. The load (not shown) is supplied from a circuit including lead 11, strip 4, strip 2 and lead 12. The strips 2 and 4 are silver flashed at the point of contact B to provide good current conductivity.

In the preferred embodiment, strip 4 is resilient and is slightly bent so that its free rest position is shown by 4'. This is done to provide a solid, dependable electrical contact at B. Otherwise strip 4 would be just barely touching strip 2 and contact might be lost due to aging or vibration. The strip 4 cannot be bent too far, though, because when strip 2 snaps away from bimetal 3 to its free rest position 2' it must also break contact with strip 4 to interrupt the circuit. If the strip 4 has a free rest position, 4', too close to the free rest position, 2', of strip 2, the circuit may not be interrupted even after snap action has occurred. Also, assuming that contact is broken, vibration might cause a circuit reset condition. The possibility of these occuring is significantly reduced by providing a free rest position for strip 2 as shown in FIG. 2 and bending strip 4 only enough to insure a good contact at B. The support for strips 2 through 4 is generally shown at 17. An eyelet 5 is riveted to hold together in a solid stack the insulating ceramics 6-9, steel washer 10 and strips 2-4. The bottom of eyelet 5 is a threaded extension, 14, to permit easy installation of the assembled circuit breaking device.

In operation the arrangement of FIG. 3 represents the on state at low temperatures since the circuit from lead 11 to lead 12 is completed through the silver flashed contacts of strips 2 and 4 at B. When heat is applied to the bimetal 3 it deflects upward toward spring 2. Spring 2 bends upward and forces resilient strip 4 to bend upward as well. The strips 2 and 3 follow the arcs shown in FIG. IfAs the snap point, P5, is reached (See FIG. I), the spring 2 snaps away from the bimetal to attain its free rest position as described in connection with, and as shown in, FIG. 2. In this position strips 2 and 4 are also no longer in contact and current flow to the load is consequently interrupted.

The strips 2 and 3 will operate as in the FIG. 2 embodiment only if the stiffness of strip 4 permits strip 2 to follow are Cl (FIG. 1) around point P4. However, if strip 4 is stiff then some point between P4 and B, depending on the stiffness, will act as the effective center for the arc formed by the movement of P1. This arc will differ from arc Cl. Such an arrangement has the advantage of little or no bending required of a stiff strip 4 since aging or vibration will not significantly affect such a stiff strip. This insures separation of strips 2 and 4 after the snap action has occurred since their free rest positions are relatively far apart. However, such an arrangement can increase friction at the point of contact between strips 2 and 4 thereby increasing the possibility of sticking. A sharper bending of the re-entrant end, 14, of strip 2 will somewhat alleviate this condition.

The embodiment of FIG. 3 is arranged to have a bimetal 3 insulated from eyelet 5 by ceramic 6. This provides for electric shock protection since no power can flow from the power supplied to the strip 2, through the bimetal 3, to the exterior of the circuit breaker at eyelet 5. This arrangement has the added feature of thermally isolating the bimetal from the equipment to which the circuit breaker is attached. Thus; ambient temperature is sensed and insulation is provided from the possibly extraneous temperature of the equipment on which the circuit breaker is mounted.

FIG. 4 shows an embodiment adapted for those applications requiring temperature sensing of the support to which the circuit breaker is attached. For example, temperature sensing of a motor housing is one such usage when the circuit breaker is screwed into the housing. The FIG. 3 embodiment, by virtue of thermal isolation of bimetal 3 from eyelet 5, has an inherent time delay in response to heat present at the eyelet 5. FIG. 4 shows an arrangement wherein the bimetal 3 is in direct contact with the eyelet 5. The circuit breaker is screwed into the piece of equipment and heat is conducted directly to the bimetal with no intervening thermal insulators. Such an arrangement, however, would subject the operator to shock hazard since the power supply is connected through strip 2, bimetal 3 and eyelet 5 to the outside of the circuit breaker. To isolate the power supply from eyelet 5 the tip of the bimetal is provided with a non-conductor 13, such as ceramic. This non-conductive tip 13 can be attached to the bimetal in many ways and no detailed description is believed necessary.

In operation, the heat from the equipment is carried to the bimetal which then deflects and causes the same movements as discussed in detail in connection with FIG. 3 to interrupt current flow to the load.

For the sake of brevity no alternatives for the geometric configurations of strip 2 shown at 14 (FIG. 1) and B (FIG. 2) have been dealt with but clearly the invention is not limited to the shown configurations. For example, it should be clear that the bend at 14 can be anything that allows the overlap of strips 2 and 3, and facilitates the sliding movement and snap action between the contacting ends of these strips. Similarly, the amount of overlap and the exact point of contact between strips 2 and 3 is dependent on how much movement is desired before the snap action as well as the chosen geometric configuration of the two strips.

Due to the very high temperatures that the circuit breaker must withstand, materials for the various components must be selected accordingly. The most vulnerable component is strip 2 since its movements and resiliency are critical to proper operation of the circuit breaker. It must retain its characteristics to provide a sliding and snap action force as well as maintain its ability to return to its free rest position. The result, ifit cannot do so, may be inadequate force to overcome sticking or insufficient movement away from bimetal 3 in FIGS. 1 and 2 and strip 4 in FIGS. 3 and 4 to interrupt the circuit. The standard material for resilient strips in low temperature circuit breakers is beryllium copper. However, its characteristics change significantly at temperatures above 400F. The invention uses stainless steel or Permanickel for strip 2 since these materials provide good electrical conductivity yet retain their characteristics at very high temperatures.

It will be apparent from the above that the advantages of the instant invention are achieved by means of a compact, simple, economical structure. Two forces instead of one are provided to cause sliding and snap action of the spring 2 and bimetal 3 to lessen the likelihood of their sticking. Also, the current carrying elements are biased so as to prevent circuit interruption before cut-off, or circuit reset after cut-off. Furthermore, the mechanical components are chosen to maintain their characteristics at very high temperatures. Finally, the invention is easily and cheaply adaptable to many different types of uses.

While but a limited number of embodiments of the present invention have been here specifically disclosed, it will be apparent that many variations, such as various arrangements and configurations of strips 2-4 on the support 1, may be made therein, all within the scope of the invention as defined in the following claims:

I claim:

1. In a temperature sensing circuit breaking device the combination comprising a support, first and second elements secured to and extending from said support, said first element being movable from a first through a second to a third position, said first element being biased toward said first position, an end thereof moving along an arc between said first and third positions; said second element comprising temperature sensitive means effective in response to a change of temperature in a given sense to move an end of said second element along a second arc and in a given direction from said first toward said third positions, said first and second arcs intersecting at said third position, said element ends engaging at said second position; and electrical contacts operatively connected to at least one of said engaging element ends to be in contact only when said element ends are engaged, whereby when said second element moves in said given direction its said end first moves said first element away from said second position toward said third position thereof and then moves out of the path of said first arc, said first element then moving to its said first position to disconnect said electrical contacts and break the circuit. 7

2. The device of claim 1 wherein the end of said first means is reentrant.

3. The device ofclaim 2 wherein said first and second elements are substantially in parallel in the same plane and the portion of said first element near its reentrant end extends beyond said second element.

4. The device of claim 1 wherein the electrical contacts are operatively connected to each of said engaging element ends.

5. The device of claim 1 further comprising a third element, said electrical contacts operatively connected to each of said first and third elements to be in contact only when said element ends are engaged.

6. The device of claim 5 wherein said second element and said support are current and heat conductive and said second element is secured to said support by a nonconductive element.

7. The device of claim 5 wherein said support and said second element, except for its engaging end, are current and heat conductive and said second element is secured in direct contact with said support.

8. In a temperature sensing circuit breaking device the combination comprising a support, a first resiliently biased element, first means having one end engaging one end of said element at an angle, said ends engaging only when said first element is in a biased state, second means to secure to said support another end of said element and another end of said means, respectively, so that the engaged ends are movable in intersecting arcs, the engaged end of said first means increasingly biasing the engaged end of said element toward the point of intersection of said arcs in response to a given temperature change, electrical contacts operatively connected to at least one of said first element and said first means to be in contact only when said ends are engaged,

whereby substantially at thepoint of intersection said engaged ends snap apart, the contacts open and the circuit is broken.

9. The device of claim 8 wherein the engaging end of said first element is reentrant.

10. The device of claim 9 wherein the portion of said first element near its reentrant end protrudes beyond said first means.

11. The device of claim 8 further including a second element secured at one end by said second means so that its other end engages said first element only when said first element and said first means are engaged, said electrical contacts operatively connected to each of said first and second elements, respectively.

12. The device of claim 11 wherein said second element is resilient and is in a resiliently biased state when engaging said first element.

13. In a temperature sensing circuit breaking device the combination comprising a support, a first resiliently biased element having a reentrant end, a temperature sensing component, means to secure to said support one end of each of said element and said component so that said reentrant end engages and overlaps the other end of said component, said ends engaging only when said first element is in a biased state, and electrical contacts operatively connected to at least one of said first element and said component to be in contact only when said first element and said component ends are engaged.

14. The device of claim 13 wherein said first element near its reentrant end protrudes beyond said compofirst element and said component are engaged. 

1. In a temperature sensing circuit breaking device the combination comprising a support, first and second elements secured to and extending from said support, said first element being movable from a first through a second to a third position, said first element being biased toward said first position, an end thereof moving along an arc between said first and third positions; said second element comprising temperature sensitive means effective in response to a change of temperature in a given sense to move an end of said second element along a second arc and in a given direction from said first toward said third positions, said first and second arcs intersecting at said third position, said element ends engaging at said second position; and electrical contacts operatively connected to at least one of said engaging element ends to be in contact only when said element ends are engaged, whereby when said second element moves in said given direction its said end first moves said first element away from said second position toward said third position thereof and then moves out of the path of said first arc, said first element then moving to its said first position to disconnect said electrical contacts and break the circuit.
 2. The device of claim 1 wherein the end of said first means is reentrant.
 3. The device of claim 2 wherein said first and second elements are substantially in parallel in the same plane and the portion of said first element near its reentrant end extends beyond said second element.
 4. The device of claim 1 wherein the electrical contacts are operatively connected to each of said engaging element ends.
 5. The device of claim 1 further comprising a third element, said electrical contacts operatively connected to each of said first and third elements to be in contact only when said element ends are engaged.
 6. The device of claim 5 wherein said second element and said support are current and heat conductive and said second element is secured to said support by a nonconductive element.
 7. The device of claim 5 wherein said support and said second element, except for its engaging end, are current and heat conductive and said second element is secured in direct contact with said support.
 8. In a temperature sensing circuit breaking device the combination comprising a support, a first resiliently biased element, first means having one end engaging one end of said element at an angle, said ends engaging only when said first element is in a biased state, second means to secure to said support another end of said element and another end of said means, respectively, so that the engaged ends are movable in intersecting arcs, the engaged end of said first means increasingly biasing the engaged end of said element toward the point of intersection of said arcs in response to a given temperature change, electrical contacts operatively connected to at least one of said first element and said first means to be in contact only when said ends are engaged, whereby substantially at the point of intErsection said engaged ends snap apart, the contacts open and the circuit is broken.
 9. The device of claim 8 wherein the engaging end of said first element is reentrant.
 10. The device of claim 9 wherein the portion of said first element near its reentrant end protrudes beyond said first means.
 11. The device of claim 8 further including a second element secured at one end by said second means so that its other end engages said first element only when said first element and said first means are engaged, said electrical contacts operatively connected to each of said first and second elements, respectively.
 12. The device of claim 11 wherein said second element is resilient and is in a resiliently biased state when engaging said first element.
 13. In a temperature sensing circuit breaking device the combination comprising a support, a first resiliently biased element having a reentrant end, a temperature sensing component, means to secure to said support one end of each of said element and said component so that said reentrant end engages and overlaps the other end of said component, said ends engaging only when said first element is in a biased state, and electrical contacts operatively connected to at least one of said first element and said component to be in contact only when said first element and said component ends are engaged.
 14. The device of claim 13 wherein said first element near its reentrant end protrudes beyond said component.
 15. The combination of claim 13 further comprising a second element secured at one end by said securing means so that its other end engages said first element only when said first element and said component are engaged, and having said electrical contacts operatively connected to each of said first and second elements, respectively, to be in contact only when said first element and said component are engaged. 